In recent years, there has been an increase in electrical loads that consume a small amount of power even when not in use. Specifically, stand-by power occurs in various electrical loads including electrical loads that await wireless signals such as imaging equipment and lighting fixtures, electrical loads that stand by for signal reception or perform signal transmission when unused such as communication devices, and electrical loads that run an internal clock when unused. In addition, some electrical loads such as television receivers and personal computers enable operating modes such as a stand-by mode and a power saving mode to be selected. In these operating modes, electrical loads enter an unused state without having their power turned off. Such operating modes also generate stand-by power. Therefore, in order to discriminate between a used state and an unused state of an electrical load by monitoring power, a magnitude of stand-by power must be known.
Stand-by power differs according to a type of an electrical load used by a power consumer and also differs according to a segment (measurement object, area) of a power distribution network in which power is to be measured. In this case, a segment of a power distribution network refers to a main circuit among a power distribution network of a consumer, a branch circuit among the power distribution network of the consumer, a room used by the consumer, an individual electrical load used by the consumer, or the like. Adopting a main circuit as a segment means that a sum of power used by all electrical loads used by the consumer is to be measured, while adopting each of a plurality of branch circuits as a segment means that a sum of power used by electrical loads connected to each branch circuit is to be measured.
As described earlier, stand-by power of an electrical load must be obtained in advance in order to discriminate between a used state and an unused state of the electrical load. For example, techniques are proposed in which a histogram of power values is created from, for example, a record of power values of the previous day, whereby a power value which is on a right side of a peak of frequency and whose frequency equals 0 or represents a local minimum value is adopted as stand-by power (for example, refer to paragraphs [0135] and [0136] in JP 2012-168018 A (hereinafter, referred to as “Document 1”)).
With the technique described in Document 1, since stand-by power is obtained using a shape of a peak of frequency in a histogram, information regarding time is not retained. Therefore, stand-by power cannot be accurately obtained when, for example, stand-by power fluctuates from one time slot to the next.